1. Field of the Invention
The field relates generally to integrated devices and methods for packaging the same. In particular, the field relates to devices and methods for improving electrical connections between integrated device packages and external devices.
2. Description of the Related Art
Integrated electronic and electromechanical devices (“integrated devices”) are used in a wide variety of products, including computers, mobile devices, automobiles, consumer electronics devices, medical devices, and many other applications. Integrated circuit dies and microelectromechanical systems (MEMS) dies are two examples of integrated device dies that can be used within a larger electrical/electronic, mechanical, or other type of system. For example, an integrated circuit die (e.g., a chip) can be used as a processor within a larger system, e.g., a mobile smartphone, tablet computer, or an automobile. In order to operate within the larger system, the integrated device die is typically packaged and configured to couple to the larger system. Often, integrated device packages (also referred to herein as “packages”) are configured to couple to a system substrate, e.g., a motherboard made of printed circuit board (PCB) material, that is in turn electrically and mechanically coupled to the larger system.
There are a variety of types of integrated device packages. For example, Quad Flat No-Lead (QFN) packages have gained popularity in recent years. A QFN package can be a leadframe based, encapsulated chip scale package that can generally comprise a square or rectangular package body with leads on four sides of the body. The package leads are exposed on the bottom surface of the package body to couple to the system substrate, e.g., a PCB substrate coupled to and situated within a larger system like an automobile or a computer. However, the packages are dubbed “no-lead” because the leads are flush with or embedded within the side surfaces of the package such that they do not protrude laterally. Other types of integrated device packages are also suitable for various applications, including ball grid array (BGA) packages, Quad Flat Packages (QFP), thin small-outline packages (TSOP), dual flat no-lead (DFN) packages, and many other types of packages.
As mentioned above, the integrated device package can be coupled to a larger system by electrically and mechanically coupling the package to a system substrate. One way to couple an integrated device package to a system substrate is using solder. In soldering techniques, exposed leads of the integrated device package can be bonded to corresponding electrical contact pads on the system substrate. For coupling surface mount components, e.g., integrated device packages, to a system substrate (e.g., a PCB substrate), reflow soldering can be used. In reflow soldering techniques, a solder paste or ball is applied to electrical contact pads on the system substrate (and/or also on the leads of the integrated device package). After contacting the leads of the integrated device package to the electrical contact pads of the system substrate, a hot reflow process is applied, during which the solder can wet various portions of the leads of the integrated device package, including exposed bottom surfaces and portions of end surfaces of the leads.
When integrated device packages are soldered to system substrates, it is important to ensure that the electrical and mechanical connection is reliable and strong. Indeed, one failure mode for electronic/electrical or electromechanical systems is the failure of solder joints connecting integrated device packages to system substrates. For example, external loads can damage the solder joint and can cause the leads of the package and the contact pads of the system substrate to mechanically decouple from one another. It can therefore be important to inspect solder joints after mounting components to the system substrate.
Alternatively, visible inspection systems, such as an automated optical inspection (AOI) system, can be employed to visually inspect the solder joints. Because surface mounted components may obscure the view of solder joints underlying the components (e.g., solder that is applied to bottom surfaces of the leads in an integrated device package), one way to estimate the reliability of a solder joint is to inspect the solder that reflows up the outer ends of the leads. For example, in some arrangements, if the solder suitably couples to certain portions of the outer ends of the leads to form a strong and reliable bond, then the user can, in some circumstances, infer that the solder bonding the bottom surface of the leads to the contact pads of the system substrate is also strong and reliable. In addition, the application of solder to the outer ends of the leads may also improve the overall solder strength because solder can be applied on a different plane, e.g., the side of the leads. Accordingly, it can be desirable to improve the adherence of solder to outer end portions of the leads in an integrated device package.